Stir together the white cake mix, flour, sugar, and salt in a large bowl until well mixed. Pour in the water, sour cream, vegetable oil, almond and vanilla extracts, and egg whites, and beat with an electric mix on low until all the ingredients are mixed and moistened but some lumps still remain, 4 minutes.

Pour the batter into the prepared cake pan, and bake in the preheated oven until the top is a light golden brown and a toothpick inserted into the center of the cake comes out clean, about 25 minutes. Allow to cool before frosting.